Anisakid larva in the viscera of a farmed Atlantic salmon (Salmo salar)

Parasitic nematodes of the family Anisakidae occur in the visceral cavity and surrounding tissues of many marine fish species at a prevalence as high as 100% in wild salmon samples. Human consumption of fish products containing these parasites can result in the zoonotic disease anisakiasis, and Anisakis simplex is most commonly associated with human disease. Previous studies of farmed salmon have found no anisakids in viscera or muscle, presumably because formulated feed production renders parasite larvae nonviable. However, among farmed Atlantic salmon (Salmo salar) examined by histopathology as part of a provincial government auditing program in British Columbia, Canada, 1 of 894 (0.11%) had an anisakid larva partly embedded in the wall of an intestinal cecum. Skeletal muscle is not examined as part of the government's program, but other studies have correlated anisakids in the viscera and muscle. Using anisakid prevalence in viscera as an estimate of its prevalence in muscle, the risk ratio of anisakid parasites in commercial product is 570 times less in farmed than in wild Atlantic salmon.     

Effects of dietary carotenoid on the gut and the gonad of the sea urchin Paracentrotus lividus

Gonad colour, determined by accumulated carotenoids, is an important marketability factor in sea urchin products. In this study, dietary carotenoids were fed to Paracentrotus lividus in prepared diets to test their effects on the sea urchin's gonad colour. All diets had the same basic content of protein, lipid, carbohydrate, ash and energy. Four diets were enriched with: (I) all-trans β-carotene; (II) astaxanthin; (III) zeaxanthin/lutein/β-carotene; and (IV) capsanthin/zeaxanthin/lutein/cryptoxanthin/β-carotene. A fifth diet had Dunaliella bardawil algal powder containing all-trans and 9-cis β-carotene added, and a sixth one was a control diet with no added carotenoids. Sea urchins were fed the control diet (no pigments) for 4 weeks, then the six experimental diets for 8 weeks. Carotenoid concentration in the gut and gonad was determined by tri-dimensional photo-diode array high performance liquid chromatography. Four qualitative colour categories were established: brown, pale yellow, medium-orange, and mango-orange.Gonad development and test diameter increased equally in all diet treatments. Carotenoid profile and concentration in the gut were higher than in the gonad or in the feed. Total carotenoid concentration was four- to ten-fold greater in the gut than in the gonad, and carotenoid profile in the gut was different from that of the diet. Gut and gonad total carotenoids, β-carotene, and echinenone concentration were not dependent on total dietary carotenoid concentration. Total carotenoid and β-carotene concentration in the gut, and total carotenoid and echinenone concentration in the gonad were significantly dependent on dietary β-carotene concentration. The percentage of gonads with acceptable colour was positively correlated with dietary and gut β-carotene concentration. Carotenoids not normally contained in the diet of P. lividus (astaxanthin, capsanthin and capsorbin), did not accumulate in the gonad. Echinenone was found in all gut and gonad samples. Over 90% of the gonads from P. lividus fed Dunaliella algal powder diet developed the optimal mango-orange colour and this diet led to the greatest echinenone concentration.     

Acoustic conditioning for recall/recapture of escaped Atlantic salmon and rainbow trout

Escape of salmon from sea cages is a problem that continues to plague the aquaculture industry. Data collected during the past 15 years from Norway, Scotland, Ireland, Canada and U.S. suggest significant impacts on natural runs of fish and economic losses to producers. The present report investigated the feasibility of using acoustic conditioning as a means of recalling/recapturing escaped fish. Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) were found to respond to frequencies in the range of 50 - 400 Hz equally well. Subsequently, both species were conditioned to a 250 Hz acoustic tone during feeding. Juvenile and sub-adult fish readily conditioned to the acoustic signal within four days, with the maximum number of fish responding (85% salmon, 96% trout) by day seven. To assess retention of conditioning, fish were exposed to a single tone without feed reinforcement every one, two or four weeks. Salmon and trout continued to respond for a seven month period with no significant decrease (88% salmon, 97% trout) in response. No significant differences were observed in the response of either species to tones differing in frequency by up to 200 Hz (89% salmon, 96% trout) and intensity by 20 dB (91% salmon, 96% trout). Both species were reproducibly recalled to a cage or feeding ring in a 3.7 m tank, but were reluctant to re-enter the cage. The findings indicate that salmon and trout are readily conditioned to acoustic signals and retain that conditioning for an extended period of time without reinforcement. These characteristics suggest that acoustic conditioning has potential as a means to recall escaped salmon and when coupled with recapture, can reduce interactions with wild stocks and losses to the producer.     

Genetic parameters for resistance to Infectious Pancreatic Necrosis in pedigreed Atlantic salmon (Salmo salar) post-smolts using a Reduced Animal Model

Infectious Pancreatic Necrosis Virus (IPNV) is an important cause of mortality and economic loss across all species of commercially farmed salmonids, and genetic variation in survival to IPN challenge has been previously demonstrated. In order to exploit this variation in the development of resistant strains, robust procedures are required to quantify the extent of genetic variation and to provide estimated breeding values used to select candidates for breeding. This paper applies a recently developed implementation of the Reduced-Animal Mixed-model procedure (RAM) to field data describing percent mortality following IPN epidemics in Scottish farmed Atlantic salmon, covering 1369 full-sib family groups distributed over four years and a total of seven sites. Pedigrees were established through a combination of electronic (PIT) tagging and parentage assignment using microsatellite DNA analysis. Heritabilities between 0.07 and 0.56 (s.e. < 0.04) were obtained, genetic correlations between sites sharing the same families were uniformly high, 0.70 to 0.85, (s.e. < 0.06) and low levels of fullsib family effect due to common environment (proportion of phenotypic variance 0.04, s.e. 0.002) were observed. These results confirmed that exploitable genetic variation exists for mortality to IPNV over a range of epidemiological conditions inherent in field data, which can be used to select strains of salmon with increased resistance to IPNV.     

Early morphological predictors of maturity in one-sea-winter Atlantic salmon

Early separation of maturing from immature fish would be very valuable in Atlantic salmon (Salmo salar) culture. Possible morphometric predictors of maturation in one sea-winter Atlantic salmon were investigated from measurements of body weight, length and depth and adipose fin length undertaken at 14 day intervals from May until August in a population of 80 individually tagged fish, 61 (male and female) of which were subsequently found to be maturing (i.e. grilse). Stepwise discriminant analysis revealed that a combination of forklength and condition factor proved to be the strongest and most consistent predictor of maturation (over 88% accurate) until August. In August when maturing fish could be easily distinguished by shape and colour, forklength and condition factor no longer had any discriminatory power, but body depth at the anal and dorsal fins were good predictors. A second trial was performed on a separate stock of fish for which the same predictors proved robust. The discriminant functions derived from one stock of fish did not, however, produce the same discriminatory power when applied to the other stock. Hence there does not appear to be a simple mathematical means for the general discrimination of maturing and immature salmon. However the morphological predictors described above could be used for visual discrimination when ‘grilse grading’.     

脂肪和蛋白质水平对工业养殖大西洋鲑消化酶、非特异性免疫及水质的影响

为探讨脂肪和蛋白质水平对工业化养殖大西洋鲑相关消化酶活力、免疫及对水质指标的影响,采用3×2双因素试验设计(3脂肪水平:18%、21%、24%,即F18、F21、F24;2蛋白质水平:38%、48%,即P38、P48),形成6种实验处理的膨化配合颗粒料,每处理3重复,在工业化封闭循环海水养殖(RAS)条件下,选用初重(650.0±45.50)g大西洋鲑720尾进行56 d的养殖实验。结果显示:(1)F21可显著提高大西洋鲑胃、肠、肝脂肪酶活力,比低脂肪分别提高11.52%、14.63%、4.31%;P48使肠、肝胰蛋白酶活力分别提高8.23%、8.33%,且发现其活力水平远高于胃蛋白酶。(2)F18、P48可显著提高肠道AKP酶活力,F18比F21、F24分别提高18.61%、31.70%,P48比P38提高13.69%。(3)F21、F24可显著改善血清的抗氧化能力,F21比F18的SOD活力提高10.32%,同时MDA含量降低4.49%;P48有利于提高血清LZM活力及补体C3含量,P48比P38分别高9.49%、5.93%。(4)低蛋白质水平可显著降低水体中氨氮、硝酸盐的含量,P38比P48分别降低61.70%、28.36%;提高脂肪水平可降低水体氨氮含量,F21、F24比F18分别降低10.00%、8.20%。研究表明,饲料脂肪和蛋白质水平与消化吸收酶、非特异免疫、养殖水氨氮之间关系特征明显;适当提高脂肪水平有利于提高消化道脂肪酶活力,提高蛋白质水平有利于提高免疫力;低蛋白质和中高脂肪组合可有效降低大西洋鲑的氨氮排泄量。     

Increased winter temperature did not affect completion of smolting in Atlantic salmon

Four groups of 1+ year-old Atlantic salmon, Salmo salar, pre-smolts were reared under various temperature regimes: constant 10 °C from November onwards; ambient temperature until either 15 December or 1 February, then 10 °C; or ambient temperature throughout (control; 2–3 °C November–March). From 20 May onwards, temperature in all groups was ambient, increasing from 10 °C to 17 °C in late July. Rearing temperature had no significant effect on either the timing of completion of smolting, or the duration of the smolt-window. Mean gill Na⁺-K⁺ ATPase activity was not significantly affected by temperature regime; it increased in all groups from < 2.0 mol Pi mg protein^–1 h^–1 (units) in January to 5–7 units in mid-April, then back to < 2.0 units in July. Survival in 96 h, 37) salinity (S) tolerance tests was similar in all groups, increasing from < 10% in early March, to > 90% from mid-April to mid-June, then decreasing to < 20% by early July. Increased winter temperature significantly increased growth and condition factor compared with the control, but during April–May all four groups exhibited similar temporary decreases in condition factor in association with the completion of smolting.     

A geostatistical approach for the stock assessment of the edible sea urchin, Paracentrotus lividus, in four coastal zones of Southern and West Sardinia (SW Italy, Mediterranean Sea)

Quantitative surveys of the edible sea urchin, Paracentrotus lividus, were conducted in four fishing zones of Sardinia (Southern Italy, Mediterranean Sea), in Autumn 2007. A total of 120 stations were geo-located along a bathymetric gradient ranging from 0 to 10 m. A geostatistical method was used to evaluate spatial patterns in density and to estimate harvestable stocks. Variographic analyses showed that the isotropic Gaussian and spherical models successfully explained the spatial structure of sea urchin assemblages in these areas. Density maps obtained by punctual kriging showed that sea urchin populations tend to be patchy rather than uniform in their density distribution. A combination of mapping and size categories was used to generate diverse scenarios of harvestable stocks (specimens ≥50 mm in diameter) before the start of the current fishing season. We conclude that the geostatistical approach, which takes into consideration the spatial autocorrelation structure of the populations in small areas, seems to be a good estimator of P. lividus density and biomass and for the assessment of its harvestable stocks, and thus provides an initial step towards a scientific approach to the management of local sea urchin fisheries.     

A radiological study on the development of vertebral deformities in cultured Atlantic salmon (Salmo salar L.)

This study investigated the development of skeletal deformities in individually tagged Atlantic salmon (n = 805) from the parr stage (Sept 2001, 70 g mean ± 34 g S.D.) until 10 month after transfer to seawater (Feb 2003, 3040 g mean ± 1097 g S.D.). A subgroup of the total population (n = 129) was radiographed as parr (Feb 2002) and again 10 months after transfer to seawater (Feb 2003). Eight percent of the males matured sexually during their first autumn in sea (jack), and were excluded from further analysis. Based on an external examination of each fish (n = 773), 1.8% (n = 14) developed skeletal deformities (0.1% operculum deformities (n = 1), 0.4% jaw deformities (n = 3), 1.3% vertebral deformities (n = 10)) during the experiment. Based on evaluation of radiographs (n = 129), the prevalence of vertebral deformities was 7.0% (n = 9) at the parr stage, and 12.4% (n = 16) 10 months after transfer to seawater. From radiographs, longitudinally compressed vertebral bodies without intervertebral spaces were classified as ankylosis and compression, longitudinally compressed vertebral bodies with intervertebral spaces were classified as compressions, and dislocated vertebral bodies with a normal morphology and without intervertebral spaces were classified as ankylosis and dislocation. Of the fish that developed deformities during the experiment, 8 had ankylosis and compressions, 7 had compressions and 1 had ankylosis and dislocation. Ankylosis and compression developed in the region between vertebrae number 1 and 16, whereas compressions developed in the region between vertebrae number 13 and 49. Most of the individuals with compression 10 months after transfer to seawater had normal vertebral columns as parr, whereas all individuals with compression and ankylosis 10 months after transfer to seawater had deformed vertebral columns as parr.     

Methionine intake affect hepatic sulphur metabolism in Atlantic salmon, Salmo salar

Atlantic salmon with body weight of 493 g were fed 6 graded levels of methionine in diets based on plant proteins for a period of 85 days with the aim to test whether methionine intake affected growth, nutrient accretion and hepatic sulphur metabolism. A negative control based on a mixture of plant proteins with low fish meal inclusion (5%) containing 1.64 g methionine 16 g^− 1 N was added five levels of dl-methionine resulting in dose levels from 1.64 to 2.98 g methionine 16 g^− 1 N. A control feed based on fish meal (26%) and plant proteins (44.9%) containing 2.30 g methionine 16 g^− 1 N was used as a control for growth performance. Feed intake and thus growth was generally lower in fish fed the plant protein based diets, while digestibility of amino acids was higher in fish fed the test diets as compared to those fed the fish meal based positive control diet. However, no significant differences in either feed intake or growth were present in fish fed either of the test diets containing graded levels of methionine. Neither carcass protein or lipid retention was affected by methionine intake as confirmed by the unaffected mRNA levels of growth hormone-insulin-like growth factor in hepatic and muscle tissues. Hepatic size as well as transsulfuration was significantly affected by methionine intake. Thus it is concluded that nutrient accretion was not the main effect of methionine intake (ranging from 35 to 90 mg fish^− 1 day^− 1). Rather methionine is essential to secure high synthesis of activated methyl groups for methylation reactions ensuring a healthy fish not developing increased liver size. Intakes exceeding 60 to 70 mg methionine daily in the fast growing seawater period results in increased transsulfuration analysed as increased hepatic taurine production keeping the hepatic free methionine constant at all intakes.     

Size heterogeneity can reduce aggression and promote growth in Atlantic salmon parr

Aggression in groups of 0+ Atlantic salmon (Salmo salar) was monitoredat weekly intervals in two tanks containing 100 fish each. Three 1 + salmonparr were added to one of these. After 5 weeks, fish weights were measuredin both tanks and the conditions reversed. At ten weeks, weights of fish inboth tanks were measured again. In both populations, levels of aggressionamong the smaller fish were significantly lower and growth ratessignificantly higher when the large fish were present. Although the largefish attacked the small ones, the rate at which they did so was an order ofmagnitude lower that the rate at which small fish attacked each other in theabsence of larger conspecifics. This raises the possibility that levels ofaggression among farmed salmon might be reduced by the addition of a fewlarge conspecifics.     

Protein and lysine requirements for maintenance and for tissue accretion in Atlantic salmon (Salmo salar) fry

Available data on the quantitative requirement for lysine (Lys) in different salmonids show much variability. So far, there are very limited data on the maintenance requirements of indispensable (I) amino acids (AA) in fish. In the present study, we determined simultaneously the Lys requirements for maintenance and for protein accretion in Atlantic salmon fry by adapting a protocol established for the piglet. Groups of fish having an initial body weight of 1.5 g were fed for 28 days on isoenergetic diets with increasing nitrogen (N) content supplied by cod meal and a mixture of crystalline AAs (50% of total dietary N). Except the protein-free diet (PF; 0.2% dry matter (DM)), the N content of the other diets was either low (2.9% DM), medium (6.2% DM) or high (8.5% DM). Two types of diets with the same N content were formulated. The AA pattern of three control diets was based on the AA pattern of the cod meal protein. For the other three diets, Lys·HCl was totally omitted from the low-N diet (LPD), and 50% of Lys·HCl was removed from the medium- and high-N diets. After a 28-day feeding trial, carcass N and Lys gains were estimated. N and Lys requirements for maintenance and for growth were calculated regressing daily N or Lys gain against N or Lys intakes. The daily N requirement for growth above maintenance was 3.05 g per g protein gain and for maintenance it was 54 mg kg body weight^− 0.75. From the regression between protein and Lys intake, we calculated that for the accretion of 1 g body protein, the dietary Lys requirement was 152 mg, and that the Lys maintenance requirement for zero N gain was 20 mg kg body weight^− 0.75/day. This last value is higher than the previous estimations obtained for rainbow trout and could be explained by the lower body weight or age of the fish used here.     

Additive effects of advanced temperature and photoperiod regimes and LHRHa injection on ovulation in Atlantic salmon (Salmo salar)

In order to evaluate manipulation of spawning time as a potential means to extend 0+ Atlantic salmon (Salmo salar) smolt production in Tasmania, Australia, female salmon were exposed to a natural/simulated natural (42°S) photoperiod or an advanced (L:D 9:15) photoperiod from the austral summer solstice (20 December) under natural or advanced (~ 6 °C below natural temperature) temperature conditions. In late summer (26 February) injections of a commercial LHRHa preparation or vehicle (propylene glycol) commenced. Regular ovulation checks were conducted and ova were fertilised using milt from LHRHa-injected males held under matching photo-thermal conditions. Plasma levels of 17β-estradiol (E₂) and testosterone (T) were monitored and reproductive success (cumulative % ovulation, % fertilisation and % survival to the eyed-egg stage) was recorded. Ovulations commenced first (09 March) in LHRHa-treated fish that experienced advanced photoperiod and thermal regimes whereas sham-treated fish exposed to natural photoperiod and temperature conditions where the last to ovulate (22 May-08 June). Treatment-related sequential changes in the timing of ovulations were reflected by sequential advances in the timing of peaks in plasma levels of E₂ and T. The fertilisation of ova from LHRHa-treated fish that experienced advanced photoperiod and thermal regimes was significantly reduced (~ 52%) relative to all other treatments (> 80%) but there were no significant treatment-related differences in the survivals of eggs to the eyed stage (~ 50-90%). Consequently, a maximum advance in the timing of median ovulation of 71 days and commercially acceptable eyed-egg yields were generated, demonstrating that combinations of photoperiod, thermal and hormone treatments may be employed to significantly extend spawning and thereafter increase the availability of 0+ smolts for grow-out.     

The effect of artificial light treatment and depth on the infestation of the sea louse Lepeophtheirus salmonis on Atlantic salmon (Salmo salar L.) culture

Two field studies were carried out with farmed Atlantic salmon (Salmo salarL.) in sea cages to examine various effects of artificial light (AL) and the vertical distribution of salmon on lice infestation.

The use of AL light caused an overall increase in lice infestation in both experiments. The first study showed that salmon held at 0–4 m depth in cages developed higher infestation than salmon held at greater depths (4–8 and 8–12 m) under both natural light (NL) and AL. In the second study, salmon maintained in 14-m deep sea cages that were exposed to AL with different light intensities. The AL treatments resulted directly in different diel and seasonal patterns of vertical distribution of the salmon and also different temporal patterns in lice infestations. So indirectly the infestation pattern appeared to be correlated with median day-time swimming depth of the salmon.     

Hyper dense vertebrae and mineral content in Atlantic salmon(Salmo salar L.) fed diets with graded levels of phytic acid

The effects of graded levels of phytic acid on skeletal development and mineral deposition were investigated in an 80 day feeding trial with Atlantic salmon (Salmo salar L.) parr. The level of phytic acid had no significant effect on the phosphorus (P) content of either whole body or vertebral column of Atlantic salmon. Negative effects of high phytic acid levels were, however, found on whole body concentration of calcium (Ca), magnesium (Mg), and in the Ca:P ratio, and in the vertebral column concentration of zinc (Zn). A novel type of vertebral pathology was observed, hyper dense (HD) vertebrae. The HD vertebrae appeared denser on radiographic images, and they consisted of a denser trabecular network than the surrounding vertebrae. The number of fish with HD vertebrae increased from initially 16% to 45-60%, with a tendency of more fish with HD vertebrae with increasing dietary phytic acid content. The HD vertebrae are described and illustrated with radiographic images, whole mount staining, and histology.     

Nutrient digestibilities and gut function in Atlantic salmon (Salmo salar) fed diets with cellulose or non-starch polysaccharides from soy

Duplicate groups of Atlantic salmon (Salmo salar), kept in saltwater, were fed fish meal based cold-pelleted diets where graded levels of native or extruded non-starch polysaccharides (NSP) from soybeans replaced cellulose, at a total NSP level of 100 g kg^− 1 for 28 days. The study also included a diet where defatted soybean meal (SBM) constituted the NSP at a level of 100 g kg^− 1 and a reference diet without NSP supplementation.The SBM diet resulted in a significant reduction in faecal dry matter content, apparent digestibilities of starch and organic material, and growth, and an increased faecal output of several elements (K, Na, Zn), compared to all the other diets. Morphological changes were only seen in the intestine of the fish fed the SBM, i.e. the diets holding purified soy-NSP did not induce enteritis. When compared to the diet without NSP, cellulose addition increased faecal dry matter, while inclusion of native soy-NSP reduced it. Dry matter in faeces and apparent digestibility of crude protein decreased in a linear manner, while the digestibility of starch and faecal output of K and Na increased linearly when native soy-NSP replaced graded levels of cellulose from 0 to 100 g kg^− 1 feed. When diets with 75 or 100 g kg^− 1 of native NSP and extruded soy-NSP were compared, fish fed native soy-NSP had reduced faecal dry matter, higher digestibility of starch, and increased faecal output of Cu, Fe, and K. Dry matter in faeces and faecal output of Cu was lower for the highest inclusion level, while digestibility of starch and faecal output of Mn and K were higher.In conclusion, soy-NSP was inert compared to the fish meal reference, with respect to nutrient digestibilities and intestinal pathologies, but affected faecal mineral excretion in Atlantic salmon.     

Safety and efficacy of emamectin benzoate administered in-feed to Atlantic salmon, Salmo salar L., smolts in freshwater, as a preventative treatment against infestations of sea lice, Lepeophtheirus salmonis (Krøyer)

The safety and efficacy of emamectin benzoate, administered in-feed to Atlantic salmon smolts, Salmo salar L., held in freshwater, was evaluated as a preventative treatment against sea lice, Lepeophtheirus salmonis, following transfer of fish to seawater.

In the safety study, salmon smolts held in freshwater were fed with diets containing emamectin benzoate at nominal doses of 0 (control), 50 (recommended dose) and 250 (5× recommended dose) μg kg⁻¹ fish day⁻¹ for 7 days (days 0–6). Actual dose rates, based on measured concentrations of emamectin benzoate in feed, differences in fish weight, and feed consumed, were 0, 54, and 272 μg kg⁻¹ day⁻¹, respectively. On day 9, fish were transferred to seawater and observed for 14 days. No differences in feeding response, coordination, behaviour, gross and histological appearance were observed between control fish and those that received 54 μg kg⁻¹ day⁻¹. Among smolts that received 272 μg kg⁻¹ day⁻¹, approximately 50% exhibited darker coloration, and one fish (1%) exhibited uncoordinated swimming behaviour. No pathognomonic signs of emamectin benzoate toxicity were identified.

In the efficacy study, smolts held in freshwater were fed an unmedicated ration (control group) or emamectin benzoate at 50 μg kg⁻¹ day⁻¹ (treated group) for 7 days (days 0–6). On day 9, fish were re-distributed to eight seawater tanks, each holding 30 control and 30 treated fish. On days 28, 56, 77 and 109, respectively, control and treated fish in two tanks were challenged with L. salmonis copepodites. When lice in each group reached chalimus stage IV, fish were sampled and the numbers of lice were recorded. Fish challenged at day 109 were sampled for the second time when lice were at the adult stage. Efficacy was calculated as the reduction in the mean number of lice on treated fish relative to the mean on control fish. Treatment with emamectin benzoate resulted in an efficacy of 85.0–99.8% in fish challenged at days 28–77, from the start of treatment, and lice counts were significantly lower (P<0.001) on treated fish than on controls. When fish challenged at day 109 were sampled at day 128, efficacy was 44.3%, but survival of chalimus to adult lice on treated fish was lower, and at day 159, efficacy had increased to 73%. These results demonstrate that treatment of salmon smolts with emamectin benzoate in freshwater was well tolerated and highly effective in preventing sea lice infestation following transfer of fish to seawater.     

Identification of differential broodstock contribution affecting genetic variability in hatchery stocks of Atlantic salmon (Salmo salar)

Supportive breeding of Atlantic salmon (Salmo salar) is commonly employed to maintain numbers of fish where the species has become locally endangered. Increasingly, one of the main aims of population management is the preservation of natural genetic diversity. If the stocks employed in supportive breeding exhibit reduced variation they can alter the natural pattern of genetic variation observed in wild populations. In northern Spain, wild adult salmon are caught every year from local rivers and artificially crossed in order to create supportive stocks. The offspring are hatchery reared until the juvenile stage, then released into the same river where their parents were caught. In the current study, our findings demonstrate that although adult broodstock exhibit a pattern of variation similar to the wild populations, variability at microsatellite loci was drastically reduced in the juveniles released into one of three rivers analyzed. The contribution of broodstock to this juvenile stock was examined by pedigree analysis. A restricted number of females contributing to the hatchery stock was identified as the main cause of loss in genetic variation, possibly due to overmaturity of some multi-sea-winter females. We suggest that better monitoring and control of parental contribution will help in solving the problem of loss of genetic diversity in hatchery populations.     

Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~ 0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9–10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon.     

Dietary fat type affects lipid metabolism in Atlantic salmon (Salmo salar L.) and differentially regulates glucose transporter GLUT4 expression in muscle

An experiment was conducted to study dietary fat type (fish oil (FO) vs. vegetable oil) effect on lipid and glucose metabolism in post-smolt Atlantic salmon. Duplicate groups of salmon were fed one of eight diets in which the two fat sources FO (long chain n-3 fatty acids, FA) or linseed oil (LO) (short chain n-3 FA) were combined in a 2 × 4 factorial design with sunflower oil (SO) (rich in n-6 FA) at inclusion levels of 0, 25, 50 and 75% of total added fat. The effects of the diets on plasma metabolites, the activity of selected enzymes involved in lipid metabolism, biometric indices and muscle glucose transporter GLUT4 expression were determined after 12 weeks of feeding. Lower viscero-somatic indices (VSI) and fatty livers were observed in fish fed LO based diets. Increasing inclusion levels of SO affected plasma glucose concentration in fish fed FO based diets, and plasma triglycerides, which decreased in a linear and quadratic pattern in fish fed FO based diets, but increased linearly in fish fed LO based diets. Specific activity of liver carnitine palmitoyl transferase I (CPT I) and glucose-6-phosphate dehydrogenase (G6PD) and plasma nonesterified fatty acids (NEFA) concentration was higher in fish fed LO based diets. Two GLUT4 isoforms I and II have been described in muscle and proved to be differentially expressed related to dietary fatty acids. In summary, dietary fat type affects lipid metabolism in post-smolted Atlantic salmon. In addition, a possibility to interfere on glucose metabolism by means of dietary fat type is discussed.